Process for improving alloys based on aluminum, zinc and magnesium, and alloys obtained thereby



United States Patent PROCESS FOR IMPROVING ALLOYS BASED ON ALUMINUM,ZINC AND MAGNESIUM, AND AL- LOYS OBTAINED THEREBY Pierre Vachet, Meudon,and Guido-Edgar Perrier, Chambery, France, assignors toPechiney-Compagnie de groduits Chimiques et Electrometallurgiques,Paris,

rance No Drawing. Filed Nov. 14, 1963, Ser. No. 323,584 Claims priority,applicafionzlrance, Nov. 15, 1962,

915,5 Claims. (Cl. 148-159) The present invention concerns a process forimproving alloys based on aluminum, zinc and magnesium, and the alloysobtained by applying this process.

Alloys are described by symbols prescribed by norm AFNOR number A 02-001of May 1944; thus the symbol A-ZG describes an alloy containingaluminum, zinc and magnesium, while the symbol A-Z4G describes an alloytheoretically containing 4% of zinc and less than 4% of magnesium, therest being made up of aluminum.

It is known that alloys of the following composition:

have average mechanical and chemical properties, which make themsuitable for many uses.

These alloys are based on aluminum, zinc and magnesium, the othercomponents being optional and being essentially intended to improve thecharacteristics of the alloy by making the grain fine, by improving thesurface of the alloy, its mechanical properties, its capacity forwelding, and its suitability for anodic oxidation and surface treatment,and by increasing resistance to corrosion, with or without tension.Components other than those mentioned above may be used to obtaincertain special properties.

These alloys have the common feature of being selfhardening; that is tosay, they gain desirable characteristics by natural aging, after beingmade into a solid solution, either by an extrusion operation or separateheat treatment in a range of temperatures from about 350 to 500 C.followed by cooling in air to room temperature or by quenching or rapidcooling.

These alloys have great plasticity immediately after solution treatment,but they continue to harden slowly thereafter. The time required toobtain the final mechanical properties, which may be up to three months,often constitutes a serious disadvantage for industrial purposes.

An attempt has therefore been made to proceed with industrial temperingtreatments, with the following results:

For alloys based on aluminum, zinc and magnesium without any copper-andwherein the zinc content is from 2% to 4.5%, the classic example beingthe alloy known as A-Z4G, no treatment of the industrial type has beenfound to be suitable, since such treatments only give metal mechanicalproperties which are far inferior to those obtained by natural aging. Itis only with artificial aging processes lasting about 200 hours at atemperature of about 100 C. that desirable properties can be obtained,but such processing is commercially undesirable.

In the case of alloys of the same type, but with a zinc content ofbetween 4.5% and 9%, some industrially applicable artificial agingtreatments may be found, but these require very exact time andtemperature controls, and the time for treatment is still relativelylong.

The present invention has for its object a process enabling an alloy ofwhich the basic components are aluminum, zinc and magnesium and whichhas undergone quenching or cooling in air, to be given mechanicalproperties similar to those obtained in several months of natural aging,but in a treatment that may be carried out within a few days andpreferably within 48 hours, and it is a related object to produce newand improved aluminum, zinc and magnesium base alloys and products bythe described process.

In accordance with the practice of this invention, from 0.005% to 0.50%of cadmium is added to the base alloy and, after the resultant alloy hasundergone a quenching or cooling in air operation, it is subjected to anartificial aging treatment at a temperature within the range of to C.for a time which may range from 0 up to 48 hours, and preferably 10 to48 hours.

The alloy according to the invention is made up as follows:

the remainder being aluminum plus small amounts of impurities.

The invention thus defined will now be explained in greater detail withthe aid of the following examples, which are given by way ofillustration, but not by way of limitation:

An alloy of the type A246 and composed of the following:

Percent Zinc 3 .5 Magnesium 2.0 Manganese 0.3 Chromium 0.15 Iron 0.20Titanium 0.20 Silicon 0.05 Aluminum 93.60

will be taken as an example; it has the following properties:

it is solution heat treated by cooling in air after being heated to atemperature of 350 to 500 C.; it has great plasticity when freshlytreated:

Breaking load R=l8 kg./sq. mm. Elastic limit E=9 kg./sq. mm. ElongationA=22% it hardens slowly after this treatment, and the followingcharacteristics are obtained after 30 to 45 days:

R=35 kg./sq. mm. E=20 kg./sq. mm. A=20% it can easily be welded, thewelded zone recovering its mechanical properties due to theself-hardening process; it has good resistance to marine corrosion.

The alloy has average resistance and great ductility.

An attempt was made to obtain the characteristics obtainable by naturalaging, by means of a rapid industrial 2. The process as claimed in claim1 in which the alloy consists esesntially of:

treatment: the following characteristics were found after Percentartificial aging for 200 hours at 100 C.: Zinc 2 to 9 Magnesium 0.5 to 3g q- Manganese 0 to 1.5 g q- Irlm- Chromium 0 to 0.5 Titanium 0 to 0.5

Silicon 0 to 1 The time required for such treatment is unacceptable Iron0 to 1 for common commercial practice. 10 Zirconium 0 to 05 In theprocess described, the above alloy was modified Copper 0 to 3 by adding0.05% of cadmium. After natural cooling, Cadmium 0005 to 0.5 the alloywas subjected to an industrial artificial aging Remaindm. aluminumplusrimpurities process lasting from about 12 to 24 hours at atemperature of 160 C. The process was effective to produce 15 3. Theprocess as claimed in claim 1 in which the alloy an alloy havingsatisfactory properties. consists essentially of:

Table I compares the effects of these artificial aging Percentprocesses, after heat treatment consisting of. heating for Zinc 2.5 to 42 hours at 425 followed by cooling in air, firstly on a Magnesium 1.5 to2.5 conventional A-Z4G alloy, of which the composition is Cadmium 0.005to 0.5 given above, and secondly on the same alloy with 0.05% Manganese0 to 0.7 of cadmium added to it; the effect produced on the alloyChromium 0 to 0.5 containing cadmium by the 24-hour artificial agingprocess Iron 0 to 0.5 at 160 C. is virtually identical with the efiectproduced Titanium- 0 to 0.5 on the conventional alloy by the 200-hourartificial aging 25 Silicon 0 to 0.5 at 100 C. Remainder aluminum plusimpurities.

TABLE I Artificial aging 12 hours at 160 0. Artificial aging 24 hours at160 0.

Alloy E R Percent A E R Percent A kgJsq. mm. kg./sq. mm. kg.lsq. mm.kg./sq. mm.

Conventional A-Z4G- 16. 9 28. 4 19. 5 17. 1 28. 6 17. 8 A-Z4G withcadmium added 25. 9 34. 4 15. 3 27.1 35. s 15. 5

The longer the time between quenching and artificial 4. An alloy havingthe following composition: aging, the more favorable is the result.Percent The amount of cadmium incorporated may be from Zinc 2 to 90.005%, constituting a minimum below which no meas Magnesium 0,5 to 3urable effect can be ascertained, to 0.5%, the upper limit Manganese 0to 1.5 above which the alloy becomes difiicult to cast. The Chromium 0 t0,5 cadmium has no perceptible undesirable effect on the Titanium 0to.0.5 welding characteristics or corrosion resistance of the al-Silicon Q t 1 loys. The alloys can still hardened by natural aging underIron 0 t 1 the same conditions as for a corresponding alloy withoutZirconium 0 t 0,5 1 cadmium. Copper 0 to 3 It will be understood thatthe invention includes the Cadmium 0.005 to 0.5

alloy and product thereof and any process in which cadmium is added toan alloy based on aluminum, zinc and magnesium with a view to permittingan artificial aging treatment of industrially acceptable duration to becarried out following a solution treatment by quenching or natural aircooling.

It will be further understood that changes may be made in the details offormulation and methods without departing from the spirit of theinvention, especially as defined in the following claims.

Weclaim:

1. In a process of heat treating an aluminum-zinc-magnesium alloywherein said alloy is solution heat treated followed by quenching or aircooling and artificial aging at a temperature within the range of100-180 C. for a time within the range of 6 and 48 hours, theimprovement comprising the addition of cadmium as an essential alloyingelement in an amount within the range of 0.005 to 0.5 percent to reducethe time required for artificially aging said alloy.

Remainder aluminum plus impurities.

in which the alloy has been subjected to a solution heat treatment stepwhich includes quenching or air cooling and which has been artificiallyaged to a temperature of Remainder aluminum plus impurities.

in which the alloy has been subjected to a solution heat treatment stepwhich includes quenching or air cooling 5 6 and which has beenartificially aged to a temperature of 2,915,390 12/1959 Criner 75142 100to 180 C. for a time within the range of 6 to 48 3,031,299 4/1962 Criner14832.5 hours.

FOREIGN PATENTS References Cited Examiner 5 476,930 12/1937 GreatBritain.

UNITED STATES PATENTS 1,785,774 12/1930 Hybinette 148--159 X DAVID RECKExamme" 2,076,577 4/ 1937 Kempf 75-146 C. N. LOVELL, Assistant Examiner.

1. IN A PROCESS OF HEAT TREATING AN ALUMINUM-ZINC-MAGNESIUM ALLOYWHEREIN SAID ALLOY IS SOLUTION HEAT TREATED FOLLOWED BY QUENCHING OR AIRCOOLING AND ARTIFICIAL AGING AT A TEMPERATURE WITHIN THE RANGE OF100-180*C. FOR A TIME WITHIN THE RANGE OF 6 AND 48 HOURS, THEIMPROVEMENT COMPRISING THE ADDITION OF CADMIUM AS AN ESSENTIAL ALLOYINGELEMENT IN AN AMOUNT WITHIN THE RANGE OF 0.005 TO 0.5 PERCENT TO REDUCETHE TIME REQUIRED FOR ARTIFICIALLY AGING SAID ALLOY.